Ceramic electronic component and method for manufacturing the same

ABSTRACT

A ceramic electronic component includes two or more electrodes  5  and  6  spaced at a predetermined distance from each other, between which a potential difference is produced in operation and a void  9  that penetrates to the outside is provided. In the void  9,  a water repellent film  10  is formed. This prevents water vapor from being absorbed in the void  9  connecting the electrodes  5  and  6,  and thereby preventing the formation of a conductive path and the occurrence of ion migration.

TECHNICAL FIELD

[0001] The present invention relates to a ceramic electronic componentsuch as a chip inductor, a ceramic capacitor, and aninductance-capacitance (LC) composite component and a method formanufacturing the ceramic electronic component.

BACKGROUND ART

[0002] In recent years, electronic equipment has been miniaturized andimproved in portability. This has created a growing demand for size andweight reduction of various kinds of electronic components to be housedin the electronic equipment. Accordingly, the electronic equipment hasbeen used in diversified environments, and thus a demand for highreliability with respect to the diversified environments also has beengrowing.

[0003] Against the foregoing background, conventionally, ceramicelectronic components have presented a problem of ion migration underhigh humidity.

[0004] Ceramic electronic components are obtained by sintering particlesof the micron orders or the submicron orders. Therefore, a sintered bodythus obtained may have many minute holes, namely, pores on the surfaceor in the inner portion. Because of this, when a ceramic electroniccomponent is allowed to stand under high humidity, water vaporpenetrates into open pores in an inner portion of a ceramic sinteredbody, which are open to the surface of the ceramic sintered body. In apore having a sufficiently small diameter, capillary condensationresults in condensing of the water vapor. Among the open pores are openpenetrating pores that penetrate between electrodes provided so as tosandwich a ceramic layer therebetween. When a voltage is applied betweenthe electrodes in a state where water droplets obtained as a result ofcondensation in the open penetrating pores establish a connectionbetween the electrodes, that is, a conductive path is formed bycondensation water, an electrode metal represented by an Ag electrode isionized to cause ion migration. When the ion migration is caused, forexample, in the case of a ceramic capacitor, the insulation resistancebetween electrodes is lowered to cause degradation in electricalcharacteristics. This problem arises not only in a component with openpores but also in a component with a void (defect) portion that extendsfrom the outside to an area between electrodes.

[0005] Conventionally, the following techniques have been adopted tosuppress this ion migration, i.e. a technique in which the entiresurface of a ceramic sintered body is coated with a synthetic resin, ora technique in which all the pores on the surface of a ceramic sinteredbody are closed with a synthetic resin or glass.

[0006] However, coating the entire surface of the ceramic sintered bodywith the synthetic resin only serves to retard the penetration of watervapor into open penetrating pores. When allowed to stand under highhumidity for a long time, the water vapor diffuses through the syntheticresin to penetrate into the open penetrating pores. Then, the watervapor is condensed by capillary condensation. This phenomenon isaccelerated and thus becomes likelier to cause condensation under hightemperatures and humidity. Water droplets obtained as a result of thecondensation form a conductive path between electrodes to cause ionmigration, thereby causing variations in electrical characteristics of aceramic electronic component, which has been disadvantageous.

[0007] On the other hand, when all the pores on the surface of theceramic sintered body are closed, the synthetic resin and the glass areused in the following manners, respectively. In the case of using thesynthetic resin, a technique is employed in which the ceramic sinteredbody is impregnated with a mixed solution of a resin and a solvent andthen cured. In the case of using the glass, a technique is employed inwhich a glass paste is printed and baked. When these techniques areemployed, cross-linking or curing of the synthetic resin is caused, orthe glass is reduced in volume when melted and sintered. This makes itvery difficult to close all the pores. Even when all the pores areclosed successfully, it is impossible to fill the entire space in thepores. Instead, voids are formed in the pores, or the pores are coatedwith a film. In this case, water vapor penetrates into the pores via thevoids or is diffused to permeate through the coating film into the poresin an inner portion of the ceramic sintering body. In some cases, whenallowed to stand under high humidity for a long time, the water vapor iscondensed in the inner portion, so that a conductive path is formedbetween electrodes to cause ion migration, which has beendisadvantageous.

[0008] In order to form the synthetic resin and the glass so that novoids are formed in the space in the pores, a method also is employed inwhich a synthetic resin component of the solution with which the ceramicsintered body is impregnated and a glass component of the glass pasteare increased in concentration. However, with increased concentration,the solution and the glass paste are increased in viscosity. This makesit very difficult to impregnate all the pores on the surface of theceramic sintered body with the solution and the glass paste. Even whenthe solution is allowed to permeate through all the pores on the surfaceof the ceramic sintered body successfully, it is impossible to allow thesolution to permeate through the pores in the inner portion of thesintered body. As described above, when a technique is limited to asimple process in which all the pores on the surface of the ceramicsintered body are closed with the synthetic resin, water vapor isdiffused through the synthetic resin to penetrate into the inner portionof the ceramic sintered body. This causes ion migration, thereby causingvariations in electrical characteristics, which has beendisadvantageous. On the other hand, when the entire surface of a ceramicsintered body is coated with glass completely, while water diffusion andpenetration can be prevented, diffusion of the glass into ceramic iscaused when the glass is baked, thereby causing variations incharacteristics. Because of this, in many cases, this technique cannotbe employed from a structural standpoint.

DISCLOSURE OF THE INVENTION

[0009] In order to solve the conventional problem, the present inventionis to provide a ceramic electronic component that allows the occurrenceof ion migration to be prevented even when allowed to stand under highhumidity for a long time, thereby preventing the degradation ofelectrical characteristics caused by the ion migration.

[0010] In order to achieve the aforementioned object, a ceramicelectronic component of the present invention includes two or moreelectrodes spaced at a predetermined distance from each other, betweenwhich a potential difference is produced in operation and a void thatcommunicates with the outside is provided. In the void, a waterrepellent film is formed.

[0011] Furthermore, a method for manufacturing the ceramic electroniccomponent of the present invention is a method for manufacturing aceramic electronic component including two or more electrodes spaced ata predetermined distance from each other, between which a potentialdifference is produced in operation and a void that communicates withthe outside is provided. In the method, a coupling agent containingfluorine is brought into contact with the void, and then dried to beheat-treated.

[0012] According to the present invention, capillary condensation is notcaused between electrodes, which is caused generally due to highhumidity, and thus a water path, namely, a conductive path in which ionscan migrate is not formed between the electrodes even when condensationis caused compulsorily due to a temperature difference, thereby allowingthe prevention of ion migration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic sectional view of a thick film ceramiccapacitor on an alumina substrate according to an embodiment of thepresent invention, in which a water repellent film is formed in anentire ceramic sintered body.

[0014]FIG. 2 is a schematic sectional view of the thick film ceramiccapacitor on the alumina substrate to show a structure according to theembodiment of the present invention.

[0015]FIG. 3 is a schematic sectional view of the thick film ceramiccapacitor on the alumina substrate according to the embodiment of thepresent invention.

[0016]FIGS. 4A to 4D are schematic sectional views showing process stepsin a method for manufacturing the thick film ceramic capacitor on thealumina substrate according to the embodiment of the present invention.

[0017]FIG. 5 is a schematic sectional view of Comparative Example 2 inwhich a thick film ceramic capacitor on an alumina substrate is coatedwith a phenol resin.

[0018]FIG. 6 is a schematic sectional view of Comparative Example 3 inwhich pores on a surface portion of a thick film ceramic capacitor on analumina substrate are closed with a silicone resin.

[0019]FIG. 7 shows a perspective view of a composite inductor componentused in Example 5 of the present invention.

[0020]FIG. 8 is an exploded perspective view of the composite inductorcomponent used in Example 5 of the present invention.

[0021]FIGS. 9A to 9E are schematic diagrams showing process, steps in amethod for manufacturing the composite inductor component used inExample 5 in the present invention.

[0022]FIG. 10 is a sectional view of the composite inductor componenttaken on line I-I of FIG. 7.

[0023]FIG. 11 is a schematic diagram of a vacuum-pressure impregnationdevice used in Example 3 and for the composite inductor component usedin Example 5 of the present invention.

[0024]FIG. 12 is a schematic sectional view of a multilayer ceramiccapacitor used in an example of the present invention.

[0025]FIG. 13 is an expanded sectional view of a multilayer ceramiccapacitor to show a structure according to an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] In the present invention, the water repellent film may be formedonly in an area between the two or more electrodes, or in all the voidsin an inner portion of the ceramic sintered body. In the case of formingthe water repellent film only in the area between the two or moreelectrodes, the water repellent film can be formed, for example, in thefollowing manner. The electronic component is immersed in a solutioncontaining a coupling agent that will be described later. Then, thecoupling agent in a surface layer portion is cleaned with a solution soas to be removed. This is followed by a drying process and heattreatment. In the case of forming the water repellent film in all thevoids in the inner portion of the ceramic sintered body, the waterrepellent film can be formed by omitting the process step of cleaningthe surface layer portion.

[0027] The water repellent film is formed of a residue resulting from amolecule of the coupling agent. Preferably, the water repellent film hassuch a thickness as not to narrow an inner portion of the void by notless than 1 nm. By a water repellent treatment, migration caused bywater is reduced. Preferably, the molecule of the coupling agent isbonded to a ceramic base material by a covalent bond. By the covalentbond, when seen from a chemical aspect, water repellency can bemaintained stably for a long time.

[0028] Furthermore, preferably, the molecule of the coupling agent has aportion containing a fluoroalkyl group. Preferably, the molecule of thecoupling agent is formed, for example, of a residue of perfluoroalkylalkylsilane represented by the following general formula (ChemicalFormula 1):

CF₃—(CF₂)_(n)—R—Si(O—)₃  (Chemical Formula 1).

[0029] (n: 0 or an integer, R: a substituent containing an alkylenegroup, or a Si or oxygen atom)

[0030] The molecule of the coupling agent containing the fluoralkylgroup may be bonded to the base material in the form of a singlemolecule. Preferably, the molecule of the coupling agent is bonded tothe base material in the form of a polymer. By polymerization, densityis increased and water repellency is enhanced.

[0031] Ceramic electronic components have been smaller and more compact,and thus microscopic defects are likely to be caused. However, suchdefects can be prevented by forming the water repellent film of thepresent invention. The water repellent film can be applied, for example,to an electronic component in which a ceramic formed body is formed byprinting and sintered. Further, the water repellent film can be appliedto an electronic component in which ceramic formed into a sheet and anelectrode layer are laminated alternately and sintered. Furthermore, thewater repellent film can be applied to an electronic component in whicha ceramic layer is formed by vapor deposition, sputtering, or the like.Moreover, the water repellent film can be applied to an electroniccomponent in which the two or more electrodes are buried in an innerportion of a ceramic sintered body or integrated on the surface of theceramic sintered body. The electronic component may be a thick filmceramic electronic component including a ceramic layer that is formed asa thick film on a base material, and at least two electrodes. Further,the electronic component may be a composite inductor component includinga ceramic sintered body and at least two conductive circuits.Furthermore, the electronic component may be a multilayer ceramiccapacitor, a varistor, a semiconductive ceramic capacitor, a ceramicthermistor, an inductor array, a common-mode choke coil, amicro-transformer, and a ceramic electronic substrate housing at leastone selected from these components.

[0032] In the method of the present invention, preferably, the couplingagent is formed of perfluoroalkyl alkylsilane containing a fluoroalkylgroup, which is represented by the following general formula (ChemicalFormula 2):

CF₃—(CF₂)_(n)—R—SiY_(q)(OA)_(3-q)  (Chemical Formula 2).

[0033] (n: 0 or an integer, R: a substituent containing an alkylenegroup, or a Si or oxygen atom, Y: a substituent of an alkyl group, OA:an alkoxy group, q: 0, 1, or 2)

[0034] The following description is directed to the case where acompound represented by the above general formula (Chemical Formula 2)is, for example, CF₃—CH₂—O—(CH₂)₁₅—Si(OCH₃)₃ (Chemical Formula 3). Anelectronic component of a ceramic base material is formed of an oxide,and thus active hydrogen exists on the surface of the electroniccomponent. Therefore, when the compound represented by (Chemical Formula3) is brought into contact with a void of the base material and heated,the compound in the form of CF₃—CH₂—O—(CH₂)₁₅—Si(O—)₃ (Chemical Formula4) is bonded to the base material by the covalent bond as a result of adealcoholation reaction. In some cases, —Si(O—)₃ is cross-linked betweenmolecules. Thus, a polymer is likely to be formed.

[0035] Preferably, the heat treatment described above is performed at atemperature of 100 to 200° C. for 5 to 60 minutes.

[0036] Furthermore, the coupling agent containing fluorine may bebrought into contact with the void by any of the following methods, i.e.vapor contact, immersion under atmospheric pressure, immersion under areduced pressure, immersion under reduced and increased pressures, spraycoating, or the like. In practice, it is preferable that the couplingagent is diluted with a solvent.

[0037] Preferably, the perfluoroalkyl alkylsilane represented by thegeneral formula (Chemical Formula 2) is at least one selected from thefollowing compounds.

[0038] (1) CF₃(CF₂)₅(CH₂)₂Si(OCH₃)₃

[0039] (2) CF₃(CF₂)₇(CH₂)₂Si(OCH₃)₃

[0040] (3) CF₃CH₂O(CH₂)₁₅Si(OCH₃)₃

[0041] (4) CF₃(CH₂)₂Si(CH₃)₂(CH₂)₁₅Si(OCH₃)₃

[0042] (5) CF₃(CF₂)₃(CH₂)₂Si(CH₃)₂(CH₂)₉Si(OCH₃)₃

[0043] (6) CF₃COO(CH₂)₁₅Si(OCH₃)₃

[0044] (7) CF₃(CF₂)₅(CH₂)₂Si(OC₂H₅)₃

[0045] (8) CF₃(CF₂)₇(CH₂)₂Si(CH₃)₂(CH₂)₉Si(OC₂H₅)₃

[0046] (9) CF₃(CF₂)₇(CH₂)₂Si(CH₃)₂(CH₂)₆Si(OC₂H₅)₃

[0047] (10) CF₃(CF₂)₇(CH₂)₂Si(OC₂H₅)₃

[0048] (11) CF₃CH₂O(CH₂)₁₅Si(OC₂H₅)₃

[0049] (12) CF₃COO(CH₂)₁₅Si(OC₂H₅)₃

[0050] Hereinafter, the present invention will be described by way ofembodiments with reference to appended drawings.

[0051] Embodiment 1

[0052]FIG. 3 is a schematic sectional view of a thick film ceramiccapacitor 1 formed on an alumina substrate. In the figure, referencenumerals 2, 3, and 4 denote an alumina substrate, a rear surfaceelectrode, and a through hole, respectively. Further, reference numerals5, 6, and 7 denote a front surface electrode (a bottom surfaceelectrode), a top surface electrode, and a dielectric layer,respectively. In the dielectric layer 7, there are provided a sinterednetwork 8 of ceramic and open penetrating pores 9 that extend to thesurface of a ceramic sintered body and between the bottom surfaceelectrode 5 and the top surface electrode 6.

[0053] In the following description, a method for manufacturing thethick film ceramic capacitor on the alumina substrate configured asdescribed above is explained with reference to the appended drawings.FIGS. 4A to 4D are diagrams showing process steps in a method formanufacturing the thick film ceramic capacitor on the alumina substrate.Initially, as shown in FIG. 4A, a paste mainly containing Ag is printedby screen printing on the alumina substrate 2 provided with a throughhole 4′ and heat-treated to form the rear surface electrode 3 having athickness of 5 μm. Concurrently with this, the through hole 4′ also isfilled with Ag to form an electrode 4. Then, as shown in FIG. 4B, apaste mainly containing Ag is printed by the screen printing on asurface opposed to the surface on which the rear surface electrode 3 isprinted and heat-treated to form the front surface electrode (the bottomsurface electrode) 5 having a thickness of 5 μm. After that, as shown inFIG. 4C, a dielectric paste 7′ is printed by the screen printing anddried. Finally, on top of the dielectric paste that has been dried, apaste mainly containing Ag and Pd is printed by the screen printing andheat-treated to form the top surface electrode 6 having a thickness of 5μm and the dielectric layer 7 having a thickness of 30 μm between thebottom surface electrode 5 and the top surface electrode 6. Theaforementioned process steps allow the thick film ceramic capacitor 1 asshown in FIG. 4D to be obtained.

[0054] In the thick film ceramic capacitor manufactured as describedabove, the electrodes are formed of Ag, and thus in forming thedielectric layer 7, firing cannot be performed at a temperature higherthan the melting temperature of Ag. Therefore, sintering of thedielectric layer 7 is hindered, so that in an inner portion of thedielectric layer 7, the sintered network 8 and the open penetratingpores 8 are formed. The sintered network 8 is a network of particlesresulting from sintering caused among the particles.

[0055]FIGS. 1 and 2 are schematic sectional views of the thick filmceramic capacitor 1 as a ceramic electronic element according to anembodiment of the present invention. In FIG. 1, a water repellent film10 is formed on the ceramic surfaces of all the open penetrating pores 9in the dielectric layer 7. In FIG. 2, the water repellent film 10 isformed on at least a portion of the ceramic surfaces of all the openpenetrating pores 9 connecting the bottom surface electrode 5 with thetop surface electrode 6.

[0056] In the following description, a method for forming the waterrepellent film of the thick film ceramic capacitor shown in FIG. 1 willbe detailed as an example. Initially, the thick film ceramic capacitor 1and a silane coupling solution in which a silane coupling agent isdissolved are prepared. The thick film ceramic capacitor is immersed inthe silane coupling solution, and an ultrasonic oscillation is appliedthereto from the outside so that the silane coupling solution is allowedto permeate through the open penetrating pores 9 in the inner portion ofthe dielectric layer 7. Then, the thick film ceramic capacitor 1 ispulled out of the silane coupling solution and heat-treated after beingair-dried at room temperature for several minutes, so that acondensation reaction of the silane coupling agent is accelerated. Thisreaction proceeds on a hydrophilic surface, and thus a hydrophobic groupderived from the above silane coupling agent is fixed on the ceramicsurfaces of the open penetrating pores 9. Thus, as shown in the figures,the water repellent film 10 is formed on the ceramic surfaces of theopen penetrating pores 9 as a result of a molecule desorbent reaction ofthe silane coupling agent. The water repellent film 10 is formed as afilm equivalent to a monomolecular layer formed by chemisorption.

[0057] In the following description, a method for forming the waterrepellent film of the thick film ceramic capacitor shown in FIG. 2 willbe detailed as an example. The thick film ceramic capacitor 1 and asilane coupling solution in which a silane coupling agent is dissolvedare prepared. The thick film ceramic capacitor 1 is immersed in thesilane coupling solution, and an ultrasonic oscillation is appliedthereto from the outside so that the silane coupling solution is allowedto permeate through the open penetrating pores 9 in the inner portion ofthe dielectric layer 7. Then, the thick film ceramic capacitor 1 ispulled out of the silane coupling solution. After that, the silanecoupling agent in the vicinity of the top surface electrode 6 is cleanedwith a solution in which the silane coupling agent can be dissolved soas to be removed. Finally, the thick film ceramic capacitor isheat-treated after being air-dried at room temperature for severalminutes, so that a condensation reaction of the silane coupling agent isaccelerated.

[0058] The aforementioned method allows a water repellent portion to beformed with reliability at least in a part of all the open penetratingpores 9 connecting the top surface electrode 6 with the bottom surfaceelectrode 5, thereby allowing ions to be prevented from migrating when avoltage is applied. In FIG. 2, the coupling agent in the vicinity of thetop surface electrode 6 is cleaned to be removed, so that in a laterprocess of finishing for the market, adherence of a coating layer to thetop surface electrode 6 and the dielectric layer 7 can be maintained,and inhibition against plating on the electrodes can be prevented.

[0059] The water repellent treatment according to the present inventionprovides ion migration suppressing action that is effective with respectto any electronic component using a metal that is suited for use as anelectrode and can be ionized. Particularly, the ion migrationsuppressing action is effective to an electronic component including anelectrode formed of an element such as Ag, Cu, and AgPd.

[0060] The following description is directed to examples in which, asshown in FIGS. 1 and 2, the water repellent film 10 is formed on theceramic surfaces of the open penetrating pores 9 between the top surfaceelectrode 6 and the bottom surface electrode 5.

EXAMPLE 1

[0061] As a water repellent agent, a compound represented by thefollowing formula (Chemical Formula 3) of a fluorine coupling agent wasprepared:

CF₃CH₂O(CH₂)₁₅Si(OCH₃)₃  (Chemical Formula 3).

[0062] Then, the compound is diluted with isopropyl alcohol to obtain asilane coupling solution containing 1% by weight of the compound. Afterthat, as described above, the thick film ceramic capacitor shown in FIG.4D was immersed in the silane coupling solution, and an ultrasonicoscillation (100 W, 45 kHz) was applied thereto for 10 minutes. Finally,the thick film ceramic capacitor was pulled out of the silane couplingsolution and heat-treated at a temperature of 150° C. for 30 minutesafter being air-dried at room temperature for 10 minutes, so that acondensation reaction of the silane coupling agent was accelerated.

EXAMPLE 2

[0063] Following the same procedure as in Example 1, an ultrasonicoscillation (100 W, 45 kHz) was applied to the thick film ceramiccapacitor. After the thick film ceramic capacitor was pulled out of thesilane coupling solution, the silane coupling agent in the vicinity ofthe top surface electrode was cleaned with isopropyl alcohol to beremoved. Finally, the thick film ceramic capacitor was heat-treated at atemperature of 150° C. for 30 minutes after being air-dried at roomtemperature for 10 minutes, so that a condensation reaction of thesilane coupling agent was accelerated.

COMPARATIVE EXAMPLE 1

[0064]FIG. 3 is a schematic sectional view of a thick film ceramiccapacitor used as Comparative Example 1. The thick film ceramiccapacitor was not subjected to a water repellent treatment.

COMPARATIVE EXAMPLE 2

[0065]FIG. 5 is a schematic sectional view of a thick film ceramiccapacitor used as Comparative Example 2. In the figure, referencenumerals 11 and 12 denote a thick film ceramic capacitor and a phenolresin, respectively. Initially, the thick film ceramic capacitor shownin FIG. 4D and the phenol resin were prepared. Then, the phenol resinwas printed by screen printing on the thick film ceramic capacitor sothat the entire surface of the thick film ceramic capacitor was coatedwith the phenol resin. Then, the phenol resin was heat-treated at atemperature of 150° C. to be cured, so that a phenol resin layer havinga thickness of about 15 μm was formed on the thick film ceramiccapacitor.

COMPARATIVE EXAMPLE 3

[0066]FIG. 6 is a schematic sectional view of a thick film ceramiccapacitor used as Comparative Example 3. In the figure, referencenumerals 13 and 14 denote a thick film ceramic capacitor and a siliconeresin, respectively. Initially, the thick film ceramic capacitor shownin FIG. 4D and a silicone resin dilute solution (a five-fold dilutesolution obtained by diluting the silicone resin with silicone oil) wereprepared. Then, the thick film ceramic capacitor was immersed in thesilicone resin dilute solution, and an ultrasonic oscillation (100 W, 45kHz) was applied thereto for 10 minutes. After that, the thick filmceramic capacitor was pulled out of the silicone resin dilute solutionand heat-treated at a temperature of 300° C. for one hour, so that poresin a surface portion of the thick film ceramic capacitor were closed.

[0067] For the respective thick film ceramic capacitors manufactured inExamples 1 and 2, and Comparative Examples 1, 2, and 3, thirty sampleswere prepared. With respect to these samples, insulation resistancebetween the top surface electrode 6 and the bottom surface electrode 5was measured after a voltage of 5 V was applied between the topelectrode 6 and the bottom surface electrode 5 for about 500 hours underan atmosphere of a temperature of 60° C. and a relative humidity of 95%.When the insulation resistance was decreased from a pre-test value ofnot less than 10 ¹⁰ Ω to not more than 10 ⁸ Ω, the insulation resistancewas regarded as being degraded. The rate of the number of samples inwhich the insulation resistance degradation was observed is shown inTable 1. TABLE 1 Sample Insulation Resistance Degradation Rate (%)Example 1 0 Example 2 0 Comparative Example 1 60 Comparative Example 230 Comparative Example 3 17

[0068] As can be seen from Table 1, in Comparative Example 1 in whichthe water repellent treatment was not performed, the insulationresistance was degraded at a considerably high rate. In ComparativeExample 2 in which the entire surface of the thick film ceramiccapacitor was coated with the phenol resin, while it was confirmed thatthe insulation resistance degradation was suppressed to some extent, theinsulation resistance could not be suppressed with respect to all thesamples. Conceivably, this is attributable to the following. Even whenthe entire surface of the thick film ceramic capacitor is coated withthe phenol resin, water vapor is diffused through the phenol resin andthereby penetrates into the open penetrating pores after a long time.Then, capillary condensation causes condensation of the water vapor.Further, in Comparative Example 3 in which the pores on the surface ofthe thick film ceramic capacitor are impregnated with the silicone resinto be closed, while a considerable effect of suppressing the insulationresistance degradation was confirmed, the degradation could not besuppressed with respect to all the samples. As in the case ofComparative Example 2, conceivably, this is attributable to thefollowing. Even when the pores in the surface portion of the thick filmceramic capacitor are closed with the silicone resin, water vapor isdiffused through the silicone resin to penetrate into the openpenetrating pores in the inner portion of the dielectric layer. Thisresults in condensation of the water vapor. It is also conceivable thatthe concentration of the silicone resin dilute solution was increased toclose the pores in the surface portion completely, so that the siliconeresin dilute solution did not permeate through the open penetratingpores in the inner portion of the dielectric layer.

[0069] On the other hand, in Examples 1 and 2 in which the waterrepellent film was formed, the insulation resistance degradation couldbe prevented completely. In the configurations of Examples 1 and 2, thesilane coupling agent is diluted to obtain a dilute solution having avery low concentration, and thus the silane coupling solution easilypenetrated into the open penetrating pores in the inner portion of thedielectric layer, so that the water repellent film is formed on theceramic surfaces of the open penetrating pores in the dielectric layer.Further, the water repellent film is only required to prevent aconductive path from being formed due to capillary condensation betweenthe electrodes having different potentials from each other, rather thanto fill the open penetrating pores physically. That is, even in a statewhere voids are formed in the open penetrating pores, the waterrepellent film performs the function sufficiently.

[0070] Conceivably, the aforementioned explains that theseconfigurations serve as effective techniques with respect to ionmigration.

[0071] Embodiment 2

[0072]FIG. 12 is a schematic sectional view of a multilayer ceramiccapacitor 41. In the figure, reference numerals 42, 43, and 44 denote adielectric layer, an internal electrode, and an external electrode,respectively. Generally, the multilayer ceramic capacitor is formed inthe following manner. A dielectric sheet manufactured by a sheet formingmethod and an internal electrode manufactured by screen printing arelaminated alternately to form one body. The body is sintered, and then,an external electrode is formed on the body.

[0073] Since the multilayer ceramic capacitor manufactured in theaforementioned manner is obtained by sintering performed at very hightemperatures, the dielectric layer is densified, so that almost no voidsare formed due to sintering performed in an incomplete manner. However,when the dielectric layer has a portion containing dust or the likebefore firing, voids (defects) are formed in the portion after thefiring.

[0074]FIG. 13 is an expanded sectional view of a multilayer ceramiccapacitor as a ceramic electronic component according to an embodimentof the present invention. A water repellent film 10 is formed on aceramic surface of an open penetrating pore 9 connecting internalelectrodes 43 a and 43 b in a dielectric layer 42.

[0075] The following description is directed to examples in which, asshown in FIG. 13, the water repellent film 10 is formed on the ceramicsurface of the open penetrating pore 9 connecting the internalelectrodes 43 a and 43 b.

EXAMPLE 3

[0076] A multilayer ceramic capacitor (rated voltage: 6.3 V, thicknessof a dielectric layer: 3 μm, an internal electrode of Ni is used) and asa water repellent agent, a compound represented by the aforementionedformula (Chemical Formula 3) of a fluorine coupling agent were prepared.Then, the compound was diluted with isopropyl alcohol to obtain a silanecoupling solution containing 1% by weight of the compound. After that, avacuum-pressure impregnation device 29 as shown in FIG. 11 was prepared.The multilayer ceramic capacitor was placed in a basket 30 in thevacuum-pressure impregnation device 29. A silane coupling solution 32was put in a container 31. Then, the vacuum-pressure impregnation devicewas depressurized (0.1 Torr) to eliminate gas remaining in the silanecoupling solution 32 and an inner portion of the multilayer ceramiccapacitor. The elimination of the gas was performed for 20 minutes.After that, in a depressurized state, the multilayer ceramic capacitortogether with the basket 30 was immersed in the silane coupling solution32 for 10 minutes. Then, an inner portion of the vacuum-pressureimpregnation device 29 was pressurized to obtain an atmospheric pressureby using N₂ gas. After that, the vacuum-pressure impregnation device 29was allowed to stand in a pressurized state (5 kgf/cm²) for 30 minutes.Then, the inner portion of the vacuum-pressure impregnation device 29was depressurized to obtain the atmospheric pressure, and the basket 30was pulled out of the silane coupling solution 32. Finally, themultilayer ceramic capacitor was taken out of the basket 30 andheat-treated at a temperature of 150° C. for 30 minutes after beingair-dried at room temperature for 10 minutes, so that a condensationreaction of the silane coupling agent was accelerated.

EXAMPLE 4

[0077] A multilayer ceramic capacitor (rated voltage: 6.3 V, thicknessof a dielectric layer: 3 μm, an internal electrode of Ni is used) and asa water repellent agent, a compound represented by the aforementionedformula (Chemical Formula 3) of a fluorine coupling agent were prepared.Then, the multilayer ceramic capacitor and the compound were placed inthe same container, and the container was heated so that the temperaturein the container was increased to 100° C. and allowed to stand for 30minutes. This heating process caused vapors to be formed from the silanecoupling agent, and the vapors penetrated into open penetrating pores inan inner portion of the multilayer ceramic capacitor. Finally, themultilayer ceramic capacitor was taken out of the container andheat-treated at a temperature of 150° C. for 30 minutes after beingair-dried at room temperature for 10 minutes, so that a condensationreaction of the silane coupling agent was accelerated.

COMPARATIVE EXAMPLE 4

[0078] A multilayer ceramic capacitor used in this example was the sameas those used in Examples 3 and 4. In this example, the multilayerceramic capacitor was not subjected to a water repellent treatment.

COMPARATIVE EXAMPLE 5

[0079] A multilayer ceramic capacitor was subjected to a water repellenttreatment in the same manner as in the water repellent treatmentperformed in Example 1 of Embodiment 1.

[0080] For the respective thick film ceramic capacitors manufactured inExamples 3 and 4, and Comparative Examples 4 and 5, thirty samples wereprepared. With respect to these samples, insulation resistance wasmeasured after a voltage of 24 V was applied to the samples for 500hours under an atmosphere of a temperature of 85° C. and a relativehumidity of 85%. When the insulation resistance was decreased from apre-test value of not less than 10⁹ Ω to not more than 10⁶ Ω, theinsulation resistance was regarded as being degraded. The rate of thenumber of samples in which the insulation resistance degradation wasobserved is shown in Table 2. TABLE 2 Sample Insulation ResistanceDegradation Rate (%) Example 3 0 Example 4 0 Comparative Example 4 7Comparative Example 5 7

[0081] As can be seen from Table 2, in Comparative Example 4 in whichthe water repellent treatment was not performed, the insulationresistance was degraded. Further, in Comparative Example 5 in which thewater repellent treatment was performed by using an ultrasonicoscillation, the insulation resistance also was degraded. Conceivably,this is attributable to the following. The dielectric layer of themultilayer ceramic capacitor was obtained by firing performed so thatthe dielectric layer was highly densified. Therefore, applying theultrasonic oscillation alone was not sufficient to allow the silanecoupling solution to permeate through defects in an inner portion of thedielectric layer. On the contrary, in Example 3 in which vacuum-pressureimpregnation was performed, and in Example 4 in which vapor impregnationwas performed, the insulation resistance was not degraded. InComparative Examples 4 and 5, upon analysis of the samples in which theinsulation resistance was degraded, it was found that a metal portionformed by migration was present in defect portions. On the contrary, inExamples 3 and 4, it was confirmed that the defect portions were presentwithout including the metal portion. This explains that the presentinvention gives the effect of preventing migration caused in a ceramicelectronic component including a defect portion, even when the ceramicelectronic component is highly densified by sintering as in a multilayerceramic capacitor.

[0082] Embodiment 3

[0083]FIG. 7 shows the appearance in perspective of a composite inductorcomponent. A composite inductor component 21 is composed of a ferritesintered body 22, and external electrodes 23 a, 23 b, 23 c, and 23 d.

[0084]FIG. 8 is an exploded view in perspective of the compositeinductor component (the external electrodes 23 a, 23 b, 23 c, and 23 dare not shown). In the figure, reference numeral 24 denotes a firstferrite sheet. Further, reference numerals 25 a, 25 b, 25 c, and 25 cdenote internal conductors. Furthermore, reference numerals 26 and 27denote a through hole filled with a conductive agent and a secondferrite sheet, respectively. The internal conductors 25 a and 25 b areconnected electrically by the through hole 26 filled with the conductiveagent. Similarly, the internal conductors 25 c and 25 d are connectedelectrically by the through hole 26 filled with the conductive agent. Noelectrical connection is established between a conductive circuit 25a-26-25 b and a conductive circuit 25 c-26-25 d. The internal conductors25 a, 25 b, 25 c, and 25 d are connected electrically to the externalelectrodes 23 a, 23 b, 23 c, and 23 d shown in FIG. 7, respectively.

[0085] In the following description, a method for manufacturing thecomposite inductor component configured as described above is explainedwith reference to the appended drawings.

[0086]FIGS. 9A to 9E are schematic diagrams showing process steps in amethod for manufacturing the composite inductor component. Initially, asshown in FIG. 9A, a plurality of first ferrite sheets 24 aremanufactured by a doctor-blade method using slurry mainly containing aferrite powder and a resin. Then, as shown in FIG. 9B, the through hole26 is formed in a center portion of the first ferrite sheet 24 byhole-forming processing and filled with a conductive material such asAg, and thus the second ferrite sheet 27 is manufactured. After that, asshown in FIG. 9C, the internal conductor 25 is formed by Ag pasteprinting or Ag plating. The internal conductor 25 is formed in the shapeof an outwardly wound spiral so that an end thereof is extended to oneend of the second ferrite sheet 27. The first ferrite sheet 24, thesecond ferrite sheet 27, and the internal conductor 25, which aremanufactured in the aforementioned manner, are laminated to form aconfiguration shown in FIG. 8, and thus a ferrite laminated body 28 ismanufactured. In this configuration, the internal conductors 25 a and 25b are laminated so that inner ends of the internal conductors 25 a and25 b are connected via the through hole 26 of the second ferrite sheet27, which is filled with the conductive material. Similarly, theinternal conductors 25 c and 25 d are laminated so that inner ends ofthe internal conductors 25 c and 25 d are connected via the through hole26 of the second ferrite sheet, which is filled with the conductivematerial. No electrical connection is established between the conductivecircuit 25 a-26-25 b and the conductive circuit 25 c-26-25 d. Then, aferrite sintered body (not shown) is obtained by firing the ferritelaminated body 28 at a temperature at which Ag of the internal conductor25 is not melted. After that, as shown in FIG. 9E, an Ag paste isapplied to end faces of the ferrite sintered body so as to be connectedto the internal conductors 25 a, 25 b, 25 c, and 25 d. Then, the ferritesintered body is heat-treated to form the external electrodes 23 a, 23b, 23 c, and 23 d. The external electrodes 23 a, 23 b, 23 c, and 23 dare processed by Ni plating followed by Sn plating, and thus thecomposite inductor component 21 is obtained. In the case of thecomposite inductor component, residual stress generated in firingbetween ferrite and the internal conductors causes degradation in theelectrical characteristics of a finished product. Therefore, firingconditions are limited, and thus open penetrating pores 9 are formed inthe ferrite sintered body.

[0087] In the composite inductor component, desired electricalcharacteristics can be obtained when the composite inductor componenthas a porosity of 2 to 30%.

[0088]FIG. 10 shows the composite inductor component as the ceramicelectronic component according to the embodiment of the presentinvention, and is an expanded sectional view of a center portion of theferrite sintered body 22 taken on line I-I of FIG. 7 showing thecomposite inductor component. A water repellent film 10 is formed on aceramic surface of an open penetrating pore 9 connecting the internalinductors 25 b and 25 c in the ferrite sintered body 22.

[0089] In the following description, a method for forming a waterrepellent film of the composite inductor component shown in FIG. 10 isdetailed as an example. Initially, the composite inductor component 21and a silane coupling agent are prepared. Then, vapor impregnation isperformed, so that the silane coupling agent is allowed to permeatethrough the open penetrating pores 9 in an inner portion of the ferritesintered body 22. After that, the composite inductor component 21 isheat-treated after being air-dried at room temperature for severalminutes, so that a condensation reaction of the silane coupling agent isaccelerated. Thus, the water repellent film 10 is formed on ceramicsurfaces of the open penetrating pores 9.

[0090] The following description is directed to examples in which, asshown in FIG. 10, the water repellent film 10 is formed on the ceramicsurfaces of the open penetrating pores 9 between the conductive circuit25 a-26-25 b and the conductive circuit 25 c-26-25 d.

EXAMPLE 5

[0091] A composite inductor component was subjected to a water repellenttreatment in the same manner as in the water repellent treatmentperformed in Example 3 of Embodiment 2.

EXAMPLE 6

[0092] A composite inductor component was subjected to a water repellenttreatment in the same manner as in the water repellent treatmentperformed in Example 4 of Embodiment 2.

COMPARATIVE EXAMPLE 6

[0093] A composite inductor component used in this example was the sameas that used in Example 5. In this example, the composite component wasnot subjected to a water repellent treatment.

COMPARATIVE EXAMPLE 7

[0094] A composite inductor component was subjected to a water repellenttreatment in the same manner as in the water repellent treatmentperformed in Example 1 of Embodiment 1.

[0095] For the respective composite inductor components manufactured inExamples 5 and 6, and Comparative Examples 6 and 7, thirty samples wereprepared. With respect to these samples, insulation resistance betweenthe conductive circuit 25 a-26-25 b and the conductive circuit 25c-26-25 d was measured after a voltage of 5 V was applied between theconductive circuit 25 a-26-25 b and the conductive circuit 25 c-26-25 dfor about 100 hours under an atmosphere of a temperature of 60° C. and arelative humidity of 95%. When the insulation resistance was decreasedfrom a pre-test value of not less than 10⁹ Ω to not more than 10⁴ Ω, theinsulation resistance was regarded as being degraded. The rate of thenumber of samples in which the insulation resistance degradation wasobserved is shown in Table 3. TABLE 3 Sample Insulation ResistanceDegradation Rate (%) Example 5 0 Example 6 0 Comparative Example 6 43Comparative Example 7 30

[0096] As can be seen from Table 3, in Comparative Example 6 in whichthe water repellent treatment was not performed, the insulationresistance was degraded at a considerably high rate. In ComparativeExample 7 in which the composite inductor component was processed in asimple manner such that the composite inductor component was immersed inthe silane coupling solution, and an ultrasonic oscillation was appliedthereto, the insulation resistance was degraded. Conceivably, this isattributable to the following. The inventors confirmed by SEMobservation that a ceramic portion of the composite inductor componentis denser compared with the thick film ceramic capacitor. Therefore,immersing the composite inductor component in the silane couplingsolution and applying an ultrasonic oscillation thereto alone was notsufficient to allow the silane coupling solution to permeate through allthe open penetrating pores in the inner portion of the ferrite sinteredbody, so that the water repellent film was not formed in some of theopen penetrating pores.

[0097] On the contrary, in the composite inductor components subjectedto a water repellent treatment by the methods employed in Examples 5 and6, the insulation resistance was not degraded. Conceivably, in thesecomponents, the water repellent film was formed on at least a portion ofthe ceramic surfaces of all the open penetrating pores.

[0098] It was confirmed that the same effect could be achieved in thefollowing components as well as in the aforementioned examples, i.e. aninductor array, a common-mode choke coil, a micro-transformer, avaristor, a semiconductive ceramic capacitor, a ceramic thermistor, anda ceramic electronic substrate housing these components.

INDUSTRIAL APPLICABILITY

[0099] As discussed in the foregoing description, the present inventionis to provide a ceramic electronic component and a method formanufacturing the ceramic electronic component. The ceramic electroniccomponent prevents a conductive path from being formed by water obtainedas a result of capillary condensation by forming a water repellent filmbetween electrodes, thereby preventing the occurrence of ion migrationresulting from the formation of the conductive path, so that insulationresistance is not degraded even under high humidity.

1. A ceramic electronic component, comprising: two or more electrodesspaced at a predetermined distance from each other, between which apotential difference is produced in operation and a void that penetratesto outside is provided, wherein a water repellent film is formed in thevoid.
 2. The ceramic electronic component according to claim 1, whereinthe formation of an electrical path is prevented by the water repellentfilm.
 3. The ceramic electronic component according to claim 1, whereinthe void is at least one selected from a minute hole and a defect. 4.The ceramic electronic component according to claim 2, wherein the waterrepellent film is formed only in the void between the two or moreelectrodes.
 5. The ceramic electronic component according to claim 1,wherein the water repellent film is formed of a residue resulting from amolecule of a coupling agent and has such a thickness as not to narrowthe void by not less than 1 nm.
 6. The ceramic electronic componentaccording to claim 5, wherein the molecule of the coupling agent isbonded to a ceramic base material by a covalent bond.
 7. The ceramicelectronic component according to claim 5, wherein the molecule of thecoupling agent has a portion containing a fluoroalkyl group
 8. Theceramic electronic component according to claim 7, wherein the moleculeof the coupling agent containing the fluoroalkyl group is a residue ofperfluoroalkyl alkylsilane represented by the following general formula(Chemical Formula 1): CF₃—(CF₂)_(n)—R—Si(O—)₃  (Chemical Formula 1). (n:0 or an integer, R: a substituent containing an alkylene group, or a Sior oxygen atom)
 9. The ceramic electronic component according to claim7, wherein the molecule of the coupling agent containing the fluoralkylgroup is polymerized.
 10. The ceramic electronic component according toclaim 1, wherein ceramic is formed by at least one selected from thegroup consisting of sintering after printing, sintering after sheetforming, vapor deposition, and sputtering.
 11. The ceramic electroniccomponent according to claim 1, wherein the two or more electrodes areburied in an inner portion of ceramic or integrated on the surface. 12.The ceramic electronic component according to claim 1, wherein theelectronic component is a thick film ceramic electronic componentincluding a ceramic layer and at least two electrodes, the ceramic layerbeing formed as a thick film on a base material.
 13. The ceramicelectronic component according to claim 1, wherein the electroniccomponent is a composite inductor component including a ceramic sinteredbody and at least two conductive circuits.
 14. The ceramic electroniccomponent according to claim 13, wherein the composite inductorcomponent has a porosity ranging from not less than 2% to not more than30%.
 15. The ceramic electronic component according to claim 1, whereinthe electronic component is at least one selected from the groupconsisting of a multilayer ceramic capacitor, a varistor, asemiconductive ceramic capacitor, a ceramic thermistor, an inductorarray, a common-mode choke coil, a micro-transformer, and a ceramicelectronic substrate housing a ceramic electronic function unitincluding two or more electrodes between which a potential difference isproduced in operation.
 16. A method for manufacturing a ceramicelectronic component including two or more electrodes spaced at apredetermined distance from each other, between which a potentialdifference is produced in operation and a void that penetrates tooutside is provided, wherein a coupling agent containing fluorine isbrought into contact with the void and subjected to a heat treatmentafter being dried.
 17. The method according to claim 16, wherein thecoupling agent is perfluoroalkyl alkylsilane containing a fluoroalkylgroup, which is represented by the following general formula (ChemicalFormula 2): CF₃—(CF₂)_(n)—R—SiY_(q)(OA)_(3-q)  (Chemical Formula 2). (n:0 or an integer, R: a substituent containing an alkylene group, or a Sior oxygen atom, Y: a substituent of an alkyl group, OA: an alkoxy group,q: 0, 1, or 2)
 18. The method according to claim 16, wherein the heattreatment is performed at a temperature of 100 to 200° C. for 5 to 60minutes.
 19. The method according to claim 16, wherein a dealcoholationreaction of perfluoroalkyl alkylsilane is caused by the heat treatment.20. The method according to claim 16, wherein the coupling agentcontaining fluorine is brought into contact with the void by at leastone selected from the group consisting of vapor contact, immersion underatmospheric pressure, immersion under a reduced pressure, immersionunder reduced and increased pressures, and spray coating.
 21. The methodaccording to claim 16, wherein the coupling agent is diluted with asolvent.